Dosnet.o is a kernel module that implements a special virtual network
device. In combination with pktdrv.c and libpacket.c, this will
enable multiple dosemu sessions and the linux kernel to be on a virtual
network. Each has it's own network device and ethernet address.

This means that you can telnet or ftp from the dos-session to your
telnetd/ftpd running in linux and, with IP forwarding enabled in the
kernel, connect to any host on your network.

If you, on the other hand, just want one DOSEMU session which talks
to your ethernet card through the packet driver, then you don't need
to use $_vnet and can set $_netdev to "eth0" or similar. Note that
this all requires root privileges because the DOSEMU code needs to
manipulate raw sockets.

Finally, start dosemu (either as root or suid-root)
and give your TCP/IP client and ip-address in the
subnet you just configured. This address should be unique, i.e. no other
dosemu, or the kernel, should have this address. For the example addresses
given above, 192.168.74.2-192.168.74.254 would be good. Now you can use a
dos telnet client to telnet to your own machine!

Allowing network access from dosemu is an important functionality.
For pc based network product developers, it will offer an easy development
environment will full control over all the traffic without having to run
around and use several machines. It will allow already available
client-server based "front-ends" to run on dosemulator. (Assuming that
they are all packet driver based -- as of now ;-) )

To accomplish that, we require independent protocol stacks to coexist
along with linux' IP stack. One way is to add independent network card.
However, it is cumbersome and allows at most only 2-3 stacks. Other option
is to use the a virtual network device that will route the packets to
the actual stacks which run as user programs.

Have a virtual device which provides routing interface at one end
(so it is a network device from linux side) and at other end, it
sends/receives packets from/to user stacks.

All the user stacks AND virtual device are virtually connected by
a network (equavalent to a physical cable). Any broadcast packet
(sent by either user stack or router interface of the virtual
device) should be sent to all the user stacks and router.
All non-broadcast packets can be sent by communicating with
each other.

Each user stack (here dosemu process) will have an base interface
which allows sending and receiving of packets. On the top of this,
a proper interface (such as packet driver interface) can be built.
In dosemu, a packet driver interface is emulated.

Generate an unique ethernet address for each dosemu .
I have used minor no. of the tty in use as part
of ethernet address. This works unless you start
two dosemu's in same tty.

Communication with dosnet device is done by opening
a SOCK_PACKET socket of special type.

IPX bridge code. Between eth0 and dsn0 so that multiple
lan accesses can be made. 0.1 is non-intelligent.
(both versions are alpha codes.)
Actually IPX routing code is there in kernel. Has anyone been
successful in using this?
Yet another alternative is to use IPTunnelling of IPX
packets (rfc 1234). Novell has NLMs for this on the netware
side. On linux, we should run a daemon implementing this
rfc.

Compile the module dosnet and insmod it, and give it an IP
address, with a new IP network number. And You have to set up
proper routing tables on all machines you want to connect to.
So linux side interface is easy to set up.

This device is assigned a virtual ethernet address, defined in
dosnet.h.

This device is usual loadable module. (Someone please check if
it can be made more efficient.) However, what is interesting is
the way it allows access to user stacks (i.e. dosemu's.) i.e.
its media interface.

A packet arrives to dosnet from linux for our virtual internal
network (after routing process). If it is broadcast packet, dosnet
should send it to all dosemu's/user stacks. If it is normal
packet, it should send it only particular user stack which has
same destination ethernet address .

It performs this process by the following method, using SOCK_PACKET
interface , (and not introducing new devices).:

The dosemu opens a SOCK_PACKET interface for type 'x' with the dosnet
device. The result of this will be an addition of entry into
type handler table for type 'x'. This table stores the type and
corresponding handler function (called when a packet of this type
arrives.)

Each dosemu will open the interface with unique 'x' .

sending packets from dosemu to dosnet

SOCK_PACKET allows you to send the packet "as is".
So not a problem at all.

dosnet -> dosemu

this is tricky. The packet is simply given by dosnet
device to upper layers. However, the upper layer calls
function to find out the type of the packet which is
device specific (default is eth_type_trans().).
This routine, which returns type of given packet, is to
be implemented in each device. So in dosnet, this plays
a special role. If the packet is identified as
type 'x', the upper layers (net/inet/dev.c) call the
type handler for 'x'.

Looking at destination ethernet address of a packet, we can say
deduct that it is packet for dosemu, and its type is
'x' (i.e. 'x' is "inserted" in dosemu's virtual ethernet
address.) Type handler function for 'x' is essentially
SOCK_PACKET receiver function which sends packet back to
dosemu.

NOTE: the "type" field is in destination ethernet address
and not its usual place (which depends on frame type.) So
the packet is left intact -- there is no wrapper function
etc. We should use type "x" which is unused by others;
so the packet can carry _ANY_ protocol since the data
field is left untouched.

Broadcast packets

We use a common type "y" for dosnet
broadcasts. Each dosemu "registers" for "y" along
with usual "x" type packet using SOCK_PACKET. This
"y" is same for all dosemu's.
(The packet is duplicated if more than one SOCK_PACKET
asks for same type. )

When a packet arrives, it arrives on one of the two
SOCK_PACKET handle we need to find out which of the
registered protocols should be handled this code.
(Earlier code opened multiple sockets, one for each IPX type.
However it is not useful now because we use *any*
type.) When a new type is registered, it is added to a
Type list. When a new packet arrives, first we find out
the frame type(and hence the position of type field in the
packet, and then try matching it with registered types.
[ ---- I missed comparing class; I will add it later.]
Then call the helper corresponding to the handle of that
type.

Rob, you should help in the following:

Packet driver code ...

We should now open only two sockets: one specific to dosemu and
other broadcast. So we have to add code to demultiplex
into packet types... I couldn't succeed. Even
broadcast packets are not getting to dosemu.

Other systems need to have route to this
"new" network. The easiest way to do this is to have static route for
dosnet IP network included in remote machine you want to connect to.
After all tests are carried out, one could include them permanently
(i.e. in gated configurations etc.). However, the "new" IP address should
only be internal to your organisation, and not allowed to route outside.
There is some rfc in this regard, I will let you know later.
For e.g., I am working on 144.16.98.20. Internal network I created was
144.16.112.0. (See the above route command.)
To connect to another linux system 144.16.98.26 from dosemu, I include
static route by running 'route add -net 144.16.112.0 gw 144.16.98.20'
on that system. It becomes more complex if you need to connect to
outside of 144.16.98.0.

Since dosemu is now on "different device", IPX needs to be either
bridged or routed. If it is bridged, then there is no requirement for
any extra administration ; simply run 'ipxbridge' program supplied with
the dosnet sources. (There are two versions of it; 0.1 copies all
packets to from/to both interface. 0.2 is "intelligent bridge", it
copies packet to other interface only if the destination lies on other
interface. )

If you instead want to use "routing" for IPX, then you need to
enable IPX config option in the kernel. Next, you should select a
network number that won't clash with others. Set up static direct
ipx routes in linux, and then in one Novell netware server which is
directly connected (i.e. without any router inbetween.). (That is where
you should contact Novell sysadm's ;-) The idea is, the server acts as route
broadcaster. (I haven't actually tested this; and we are working on getting
proper daemons etc. which will make linux act as IPX router proper.)

(You could include this info along with other documentation...)

Hope this helps,

Vinod.

I just realised one more thing: The ipxbridge-0.2 code assumes that
you have 'eth0' and 'eth1' as the two interfaces. And it uses this
fact while choosing the interface to put the packet. So it won't
recognise when 'dsn0' is used.